This invention relates to the field of optical inspection systems. More particularly, this invention relates to an inspection system that uses time delay integration sensors for optical inspection of integrated circuit substrates.
The integrated circuit fabrication industry relies on continual and repeated inspection of integrated circuits as they are produced to ensure that the processes are operating properly and that the integrated circuits themselves are properly formed. Automated visual inspection of integrated circuit substrates has become a standard step in this process. Automated visual inspection is accomplished by illuminating a substrate with light emanating from a controlled illuminator, and constructing an image of the surface based on the light that is reflected off the surface and toward a light sensor. The image is then processed to detect defects on the substrate surface.
Time delay integration sensors are often used as the optical sensor in automated substrate review. Time delay integration sensors tend to exhibit relatively lower noise and produce higher quality images than other types of sensors, especially under low light conditions. Thus, time delay integration sensors tend to exhibit a higher sensitivity to defects than other sensors, such as linear detection systems. This is because time delay integration techniques permit longer effective exposure times than linear detection sensors.
Integrated circuit substrate inspection has traditionally been performed using a system employing a single time delay integration module, consisting of the time delay integration sensor and associated electronic components that are mounted on a shared circuit board. The substrate, residing on a traveling stage, is indexed underneath the sensor in the x-direction. The sensor only resolves a partial width, or swath, of the substrate as it travels underneath the sensor on the stage. The sensor resolves a single image of the swath created during each pass of the substrate past the sensor. The substrate is then indexed in the y-direction and the sensor takes another image swath as the substrate travels back underneath the sensor in the x-direction. The process is repeated until as much of the substrate as desired, such as the entire substrate, has been imaged.
As the rate at which the production of integrated circuits increases, integrated circuit manufacturers look for ways to increase the speed at which the inspection processes are conducted. Typically, time delay integration systems have been sped up with the use of either a faster sensor which can handle increased stage indexing speeds, or a wider sensor that creates a wider swath and thus produces a larger image. However, these modifications require design and development of new supporting electronics and mechanical infrastructure for the automated inspection system. For example, speeding up the stage travel may require upgraded electronics to shift the active pixel line in the sensor at the increased rate. However, the sensor may not be able to adequately resolve images at the new rate. Installing a larger, faster, or more sensitive sensor also requires new supporting electronics, as well as hardware modifications. This design and development process is both expensive and time consuming.
What is needed, therefore, is a scalable time delay integration imaging system such that the effective speed at which the substrates are inspected can be readily increased as desired without new development.
The above and other needs are met by a scalable imaging system adapted to detect defects on a surface of a substrate using time domain integration sensors. A plurality of sensor module ports are disposed on an imaging platform. Sensor modules are removably connected to the sensor module ports, where the sensor modules are adapted to optically sense swaths on the surface of the substrate. Each of the sensor modules includes a time domain integration sensor, optics, an analog controller, and a digital controller. The time domain integration sensor optically senses the swath, and has a first width. The optics focus light from the swath on the time domain integration sensor. The analog controller is disposed adjacent the time domain integration sensor and receives analog signals from the time domain integration sensor and provides data signals. The digital controller receives the data signals from the analog controller, integrates the data signals into an image of the swath, and provides the image as digital signals to the sensor module port. A master controller receives the digital signals from the sensor module ports, composites the digital signals into a single image of a desired portion of the surface of the substrate, and detects defects within the image of the desired portion of the surface of the substrate. A stage moves the substrate under the sensor modules under the control of the master controller, until the desired portion of the surface of the substrate has been imaged.
In this manner there is provided an instrument that is scalable in regard to the number of time delay integration sensor modules that are used during the inspection process. As few as one sensor module may be used, in which case an increased number of passes of the stage is required to image the entire surface of the substrate being inspected. However, additional sensor modules may be plugged in to the sensor module ports provided on the imaging platform, and when additional sensor modules are plugged in, the master controller automatically recognizes the additional sensor modules, and integrates the images which they produce into the overall image of the substrate that is produced. Thus, the number of substrate passes that is required to image the entire surface of the substrate is reduced with each additional sensor module that is added to the scalable instrument. However, recalibration or realignment or other difficult integration is not required, because each of the time delay integration sensor modules functions individually until a level at which the images that they produce are composited by the master controller.
In various preferred embodiments, the desired portion of the surface of the substrate is all of the surface of the substrate. Preferably, the swaths optically sensed by the sensor modules overlap one with another. The time domain integration sensors of the sensor modules are not aligned one with another in one embodiment, and in an alternate embodiment the time domain integration sensors of the sensor modules are aligned one with another. Preferably, the master controller is further adapted to automatically receive the digital signals from a new sensor module when it is connected to one of the sensor module ports and composite the digital signals into the image of the desired portion of the surface of the substrate. Increasing a number of sensor modules connected to the sensor module ports preferably decreases a number of passes of the stage required to image the desired portion of the surface of the substrate.
In one embodiment there is a given number of sensor module ports and the given number of sensor modules connected to the sensor module ports sufficient to image all of the surface of the substrate in a single pass of the stage. Preferably, the sensor module ports are disposed side by side in two lines disposed on either side of and parallel to a travel axis of the stage. Most preferably the sensor module ports are disposed side by side in two lines disposed on a left side and a right side of a travel axis of the stage. The sensor module ports on the left side are offset such that when all of the sensor module ports on the left side of the travel axis are filled with sensor modules, all of a left side of the surface of the substrate is imaged in a single pass of the stage Similarly, the sensor module ports on the right side are offset such that when all of the sensor module ports on the right side of the travel axis are filled with sensor modules, all of a right side of the surface of the substrate is imaged in a single pass of the stage.
Preferably, the time domain integration sensor, the optics, and the analog controller of a given one of the sensor modules are all disposed on a single circuit board and the digital controller of the one of the sensor modules is not disposed on the circuit board. The time domain integration sensor is preferably disposed along a given edge of the circuit board, and the time domain integration sensors of sensor modules disposed in adjacent sensor module ports are offset one from another by no more than a width of the time domain integration sensors.